The present embodiments relate to methods of at least partially removing snow and ice from an impinger of an impingement apparatus.
Commercial cooling apparatus, such as commercial freezers, typically rely on the transfer of heat from an item, such as a food product, that is to be chilled or frozen by using a fan or blower. In many instances, the fan or blower is situated near a conveyer belt upon which the item is being carried. The item entering the freezer has a boundary layer of air surrounding it which insulates the item from the surrounding atmosphere. Traditional freezers have employed blowers that generate currents of cooling vapor in many directions. However, a significant portion of the cooling vapor does not contact the item, and in many instances does not contact the item in a direction transverse to the item's movement, such as in a perpendicular direction. Under these conditions, the cooling vapor which does contact the item often does not possess sufficient energy to substantially reduce the thickness of the boundary layer at or around the surface of the item. Therefore, there has been a need to generate directed jets of cooling vapor to disturb the boundary layer and increase heat transfer at the item.
Previous attempts to generate directed jets of cooling vapor to the item have included using a plurality of vertical tubes to provide a unidirectional air flow toward the item, and the use of a plurality of nozzles along the pathway of an item for delivering discrete jets of unidirectional cooling air. However, the use of tubes or nozzles to direct air in a cooling or freezing device has met with only limited success due to the build-up of condensation in the form of snow and/or ice in the tubes or nozzles. Such build up quickly reduces the efficacy of the cooling or freezing devices.
Another previous attempt included heating or cooling an item on a moving substrate in which a continuous channel traversing at least a major portion of the width of the moving substrate converts multi-directional flow into unidirectional flow. However, this attempt suffers from having such an increased rate of flow that the items become entrained in the flow, and, consequently, controlled processing of the item through the device becomes difficult.
Increasing the velocity of the stream of cooling vapor (such as a cryogen) which impinges the item will increase the average heat transfer coefficient in a linear manner. At a certain point, however, unless the impingement stream of cooling vapor is carefully controlled, its velocity may be sufficient to damage the item, or to displace the item from and carry same off the conveyor, and into undesirable locations elsewhere in the freezer.
The total heat transfer rates are dependent on local heat transfer coefficients. That is, the amount of heat transferred from the items to the coolant is dependent on the rate of heat transfer locally between the coolant and the item. Local heat transfer rates can be changed by controlling the distance from the source of impingement stream to the item, the velocity of the impingement stream, the turbulence in the impingement stream, and the efficiency of the flow of coolant for the impingement stream.
Heat transfer and coolant flow may be adequately controlled by using an impingement apparatus comprising an impinger, such as an impingement plate, having openings to direct the flow of coolant. Over time during operation of such an impingement apparatus, snow and ice accumulate and may build up on the impinger, thereby reducing the efficiency of heat transfer provided by the impingement apparatus. In order to at least partially remove snow and/or ice from the impinger, vibration has been used to break up the snow and/or ice, which is then free to pass through the impinger, at least partially restoring the efficiency of the impingement apparatus. Some impingement apparatus may provide high pressure differentials on opposing sides of the impinger. In these instances, the high pressure differential may dampen vibration imparted to the impinger, reducing the effectiveness of the vibration to break up snow and/or ice on the impinger.
What is needed is a means by which snow and ice may be at least partially removed from an impinger which experiences a high pressure differential on opposing sides of the impinger.